Com/iphone method of making superoleophobic re-entrant resist structures

ABSTRACT

A device and method for preparing a device having a superoleophobic surface are disclosed. The method includes providing a substrate; coating a lift-off resist layer on the substrate; baking the lift-off resist layer; layering a photoresist layer on the lift-off resist layer; performing photolithography to create a textured pattern in the photoresist layer and the lift-off resist layer, and chemically modifying the textured pattern to create a superoleophobic surface.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a division of, and claims the benefit of priorityto, U.S. patent application Ser. No. 13/550,169 (Attorney Docket No.20111081US01-0430423), filed Jul. 16, 2012, the entire contents of whichis incorporated herein by reference.

BACKGROUND

Disclosed herein is a process for preparing a device having asuperoleophobic surface comprising providing a substrate; usingphotolithography to create a textured pattern on the substrate whereinthe textured pattern comprises polymeric overhang structures; andchemically modifying the textured surface by disposing a fluorinatedcoating thereon; to provide a flexible device having a superoleophobicsurface. The flexible, superoleophobic device can be used, for example,as a front face surface for an ink jet printhead.

Fluid ink jet systems typically include one or more printheads having aplurality of ink jets from which drops of fluid are ejected towards arecording medium. The ink jets of a printhead receive ink from an inksupply chamber or manifold in the printhead which, in turn, receives inkfrom a source, such as a melted ink reservoir or an ink cartridge. Eachink jet includes a channel having one end in fluid communication withthe ink supply manifold. The other end of the ink channel has an orificeor nozzle for ejecting drops of ink. The nozzles of the ink jets may beformed in an aperture or nozzle plate that has openings corresponding tothe nozzles of the ink jets. During operation, drop ejecting signalsactivate actuators in the ink jets to expel drops of fluid from the inkjet nozzles onto the recording medium. By selectively activating theactuators of the ink jets to eject drops as the recording medium and/orprinthead assembly are moved relative to one another, the depositeddrops can be precisely patterned to form particular text and graphicimages on the recording medium.

One difficulty faced by fluid ink jet systems is wetting, drooling orflooding of inks onto the printhead front face. Such contamination ofthe printhead front face can cause or contribute to blocking of the inkjet nozzles and channels, which alone or in combination with the wetted,contaminated front face, can cause or contribute to non-firing ormissing drops, undersized or otherwise wrong-sized drops, satellites, ormisdirected drops on the recording medium and thus result in degradedprint quality. Efforts to address these issues have relied uponprinthead front face coatings. Current printhead front face coatings aretypically sputtered polytetrafluoroethylene coatings. When the printheadis tilted, the UV gel ink at a temperature of about 75° C. (75° C. beinga typical jetting temperature for UV gel ink) and the solid ink at atemperature of about 105° C. (105° C. being a typical jettingtemperature for solid ink) do not readily slide on the printhead frontface surface. Rather, these inks flow along the printhead front face andleave an ink film or residue on the printhead which can interfere withjetting. For this reason, the front faces of UV and solid ink printheadsare prone to be contaminated by UV and solid inks. In some cases, thecontaminated printhead can be refreshed or cleaned with a maintenanceunit. However, such an approach introduces system complexity, hardwarecost, and sometimes reliability issues.

There remains a need for materials and methods for preparing deviceshaving superoleophobic characteristics. Further, while currentlyavailable coatings for ink jet printhead front faces are suitable fortheir intended purposes, a need remains for an improved printhead frontface design that reduces or eliminates wetting, drooling, flooding,and/or contamination of UV or solid ink over the printhead front face.There further remains a need for an improved printhead front face designthat is ink phobic, that is, oleophobic, and robust to withstandmaintenance procedures such as wiping of the printhead front face. Therefurther remains a need for an improved printhead front face design thatis superoleophobic. There remains a further need to develop simple,cost-effective processes to create superoleophobic textures on largearea flexible substrates.

SUMMARY

Disclosed herein is a method for preparing a device having asuperoleophobic surface, the method comprising providing a substrate;coating a lift-off resist layer on the substrate; drying the lift-offresist layer; layering a photoresist layer on the lift-off resist layer;performing photolithography to create a textured pattern in thephotoresist layer and the lift-off resist layer, and chemicallymodifying the textured pattern.

Further disclosed herein is a method for preparing a device having asuperoleophobic surface, the method comprising providing a substrate;optionally coating a silicon layer on the substrate; coating a lift-offresist layer on the substrate; baking the lift-off resist layer;depositing a photoresist on the baked lift-off resist layer to create alayered structure; baking the photoresist layer; exposing thephotoresist layer to UV radiation; optionally baking the exposedphotoresist layer; developing the photoresist layer; developing thelift-off resist layer to create a textured pattern; optionally etchingthe textured pattern; and modifying a surface of the textured pattern tocreate a superoleophobic surface.

Also disclosed is a device comprising a substrate; a lift-off resistlayer; a photoresist layer, wherein the lift-off resist layer and thephotoresist layer comprise a textured pattern; and an oleophobic coatingdisposed on the textured pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron micrograph image of a textured pattern.

FIG. 2 is a scanning electron micrograph image of a single overhangre-entrant structure.

FIG. 3 is a scanning electron micrograph image of a side view of asingle overhang re-entrant structure.

FIG. 4 is a scanning electron micrograph image of a side view of atextured pattern.

FIGS. 5-8 illustrate a process for creating a textured pattern.

FIG. 9 is a photograph showing the static contact angle for hexadecaneon a fluorosilane-coated textured surface comprising overhangstructures.

EMBODIMENTS

“Superoleophobic” as used herein refers, for example, to when a dropletof hydrocarbon-based liquid, for example, ink, forms a contact-anglewith a surface that is greater than about 150°, such as from greaterthan about 150° to about 175°, or from greater than about 150° to about160°. “Superoleophobic” also refers, for example, to when a droplet of ahydrocarbon-based liquid, for example, hexadecane, forms a sliding anglewith a surface of from about 1° to less than about 30°, or from about 1°to less than about 25°, or a sliding angle of less than about 25°, or asliding angle of less than about 15°, or a sliding angle of less thanabout 10°. Oleophobic coating as used herein can be described as thecoating on which a droplet of hydrocarbon-based liquid, for example,hexadecane, forms a contact angle of larger than about 55°.

Disclosed herein is a method for preparing a device having asuperoleophobic surface, the method comprising providing a substrate;coating a lift-off resist layer on the substrate; drying the lift-offresist layer; layering a photoresist layer on the lift-off resist layer;performing photolithography to create a textured pattern in thephotoresist layer and the lift-off resist layer, and chemicallymodifying the textured pattern.

Any suitable material can be selected for the substrate describedherein. For example, the substrate may be a silicon wafer. In addition,the substrate may be a flexible substrate. The flexible substrate may beplastic, and may be selected from among, for example, a polyimide film,a polyethylene naphthalate film, a polyethylene terephthalate film, apolyethersulfone film, or a polyetherimide film, and the like, or acombination thereof. In addition, the substrate may be metal, forexample, stainless steel. The stainless steel may also be a flexiblesubstrate. The substrate may be a glass substrate, and may also beflexible.

The substrate can be any suitable thickness. The substrate may have athickness of from, for example, about 5 micrometers to about 100micrometers, or from about 10 micrometers to about 50 micrometers.

A silicon layer may optionally be deposited onto the substrate by anysuitable method. The silicon thin film may be deposited using, forexample, sputtering or chemical vapor deposition, very high frequencyplasma-enhanced chemical vapor deposition, microwave plasma-enhancedchemical vapor deposition, plasma-enhanced chemical vapor deposition,use of ultrasonic nozzles in an in-line process, and the like, amongothers. A silicon layer would not be necessary if the substrate is asilicon substrate.

The layer of silicon can be any suitable thickness. The silicon layercan be deposited onto the flexible substrate at a thickness of from, forexample, about 500 to about 5,000 nanometers, from about 1,000 to about4,000 nanometers, or from about 2,000 to about 3,000 nanometers.

A lift-off resist layer may be coated directly on the substrate or onthe silicon layer. A lift-off resist layer refers, for example, to aresist material that may or may not be photosensitive. For example, thelift-off resist layer may be a layer based on polymethylglutarimide(PMGI) or poly(methyl methacrylate) (PMMA), or any other material that,when forming a bilayer structure with a photoresist, has a differentsolubility from the photoresist in selected solvents under certainprocess conditions.

The lift-off resist layer may be dissolved in any suitable solvent inorder to coat the lift-off resist on the substrate or the silicon layer.Suitable solvents include, for example, cyclopentanone, isopropanol, orpropylene glycol monomethyl ether acetate.

The lift-off resist layer may be coated onto the substrate or thesilicon layer by any suitable method, for example by solutiondeposition. Solution deposition includes, for example, spin coating, dipcoating, spray coating, slot die coating, flexographic printing, offsetprinting, screen printing, gravure printing, or inkjet printing.

After coating the lift-off resist layer on the substrate or the siliconlayer, the lift-off layer is baked to evaporate the solvent from thelift-off resist layer. The lift-off resist layer may be baked at anytemperature that allows for evaporation of the solvent and that does notalter the properties of the substrate or silicon layer or the substrate.For example, the lift-off resist may be baked at temperatures from about140° C. to about 200° C., such as from about 150° C. to about 190° C.,or from about 160° C. to about 185° C. The baking can occur for anylength of time necessary for removal of the solvent. For example, thelift-off resist layer may be baked for 1 minute to about 30 minutes,from about 3 minutes to about 20 minutes, or from about 5 minutes toabout 10 minutes. Examples of baking techniques may include thermalheating, for example, heating with a hot plate, an oven, or infra-red(“IR”) radiation.

After baking the lift-off resist layer, a photoresist layer is depositedonto the baked lift-off resist layer. The photoresist layer may be apositive or negative photoresist. A positive photoresist refers, forexample, to a type of photoresist in which a portion of the photoresistthat is exposed to light, for example, ultraviolet (UV) light, becomessoluble to a photoresist developer. A portion of the photoresist that isunexposed to light remains insoluble to a photoresist developer.Examples of positive photoresists include, for example, OiR620-7i,Shipley 1800 Series, Rohm & Haas Megapsit SPR220 Series. In addition, ingeneral, any positive photoresists based on photodefinable epoxies,photodefinable polyimides, and photodefinable PBO (polybenzobisoxazole)would function for the current purpose. Exemplary materials includepositive-tone photoresists HD-8800 series available from HD MicroSystemsof Parlin, N.J., or the like. A negative photoresist refers, forexample, to a photoresist in which a portion of the photoresist that isexposed to light, for example UV light, becomes insoluble to aphotoresist developer. The unexposed portion of the photoresist isdissolved by a photoresist developer. Examples of negative photoresistinclude, for example, photodefinable epoxies or negative-tonephotosensitive polyimides, and related compounds known to the art.Exemplary materials include Microchem SU-8 resist. Another example isnegative-tone photodefinable polyimide precursor HD-4100 series,available from HD MicroSystems of Parlin, N.J. Another example isphotosenstive CYCLOTENE 4000 Series resin, available from Dow ChemicalCompany of Midland, Mich., and the like. Desirably, the photoresist isnot the same as the material as the lift-off resist layer.

The photoresist may be dissolved in any suitable solvent, for coatingthe photoresist layer on the baked lift-off resist layer. For example,the photoresist may be dissolved in any of the solvents described above.However, it is preferred that the lift-off resist does not, or onlypartially, dissolves in the solvent used for the photoresist. Forexample, the photoresist and lift-off resist would be immiscible. Thesolvent for photoresist depends on the photoresist used, and theappropriate solvents to use are known in the art.

The photoresist layer may be deposited by any known method, for example,by solution deposition described above. After deposition, thephotoresist layer is baked to evaporate the solvent. The photoresistlayer may be baked at any temperature that allows for evaporation of thesolvent and that does not alter the properties of the lift-off resistlayer, the silicon layer, or the substrate. For example, the lift-offresist may be baked at temperatures from about 90° C. to about 120° C.,such as from about 100° C. to about 115° C. The baking can occur for anylength of time necessary for removal of the solvent. For example, thelift-off resist layer may be baked for 1 minute to about 5 minutes, suchas from about 2 minutes to about 4 minutes. Examples of bakingtechniques are described above.

After baking, photolithography may be used to create a textured patternin the photoresist layer and the lift-off resist layer. Photolithographyinvolves exposing at least a portion of the photoresist layer or atleast a portion of the photoresist layer and at least a portion of thelift-off resist layer to light, for example, UV light, then developingthe exposed photoresist layer and lift-off resist layer or the exposedphotoresist layer and the exposed lift-off resist layer. The exposing ofthe photoresist layer and the lift-off resist layer may occursimultaneously or in separate exposing steps. In addition, thedeveloping of the photoresist layer and the lift-off resist layer mayoccur simultaneously or in separate development steps.

The exposure involves using a mask to selectively expose a portion ofthe photoresist layer and the lift-off resist layer to UV radiation, forexample, to create a pattern in the photoresist layer and the lift-offresist layer. A mask is any suitable material that does not allow light,for example, UV light to penetrate the mask. The mask may be, forexample, a glass substrate coated with a Cr layer with an etchedpattern, or a polymer substrate coated with a darkened film with apattern.

The photoresist layer may be exposed, for example, to UV radiation andthe photoresist layer and the lift-off resist layer may besimultaneously developed, or the photoresist layer may be exposed to UVradiation, then the photoresist layer may be developed, followed bydevelopment of the lift-off resist layer. Alternatively, the photoresistlayer may be exposed to UV radiation, and then following UV exposure ofthe photoresist layer, the photoresist layer may be developed. Afterdevelopment of the photoresist layer, the lift-off resist layer isexposed to UV radiation, and then following UV exposure of the lift-offresist layer, the lift-off resist layer is developed.

In addition, after exposure of the photoresist layer to UV radiation,but before the photoresist layer is developed, the exposed photoresistlayer may optionally be baked. The type of photoresist selecteddetermines if this optional step is needed, and would be known at thetime of selection of the photoresist. For example, for a positivephotoresist, this optional baking step may be used to create a smoothsurface of the sidewall of photoresist layer. For a negativephotoresist, this baking is usually necessary to drive to completion thereaction initiated by exposure described above. For example, the exposedphotoresist may be baked at a temperature that is about the same aspre-exposure bake. The baking can occur for any length of time necessaryto eliminate the sidewall roughness, sometimes referred to in the art asthe “standing wave effect” of a positive photoresist or to complete thereaction of the negative photoresist. For example, the exposedphotoresist layer may be baked for 1 minute to about 30 minutes, such asfrom about 3 minutes to about 20 minutes, or from about 5 minutes toabout 10 minutes. Examples of baking techniques are described above.

As described above, after exposure of the photoresist layer or thephotoresist layer and the lift-off resist layer to UV radiation, thephotoresist layer and the lift-off resist layer are developed.Developing removes any portion of the photoresist layer and the lift-offresist layer that is soluble in the developer. The photoresist layer andthe lift-off resist layer may be developed according to methods known inthe art. For example, if a positive photoresist is used for thephotoresist layer, after exposing a portion of the photoresist layer toUV radiation, the exposed portion becomes soluble in a first developingsolution. The developing solution is applied to the photoresist layer toremove the solubilized portion of the photoresist layer. The type ofdeveloping solution used to remove the exposed portion of thephotoresist layer depends on the particular photoresist used for thephotoresist layer and this relationship is known in the art. Forexample, the developer may be an organic developer such as a sodiumhydroxide containing developer or a metal-ion free developer such astetramethylammonium hydroxide.

After removal of the solubilized portion of the exposed photoresistlayer, a second developing solution may be applied to remove a portionof the lift-off resist layer. The lift-off resist layer is soluble inthe second developer. The second developing solution may be the same asor different from the first developing solution. If the seconddeveloping solution is the same as the first developing solution,removal of the solubilized portion of the exposed photoresist layer anda portion of the lift-off resist layer may occur in the same step,meaning that a second application of the first developer may not beneeded. It is known in the art that the length of time the lift-offresist layer is exposed to the developer determines how much of thelift-off resist layer is removed by the developer. For example, thelift-off resist layer may be exposed to the developer for about 15seconds to about 2 minutes, such as for about 30 seconds to about 90seconds, or from about 45 seconds to about 1 minute in order to create are-entrant structure. Removal of the solubilized portion of the exposedphotoresist layer and a portion of the lift-off resist layer may createa re-entrant structure.

However, it is known in the art that the baking temperature and thebaking time will determine the dissolution rate of the lift-off resistlayer in the developer. For example, a longer baking time and/or highertemperature results in drier and denser film and would decrease thedissolution rate. Thus, the lift-off resist layer may need to bedeveloped for a longer or shorter time the more the dissolution rate isdecreased or increased, respectively. The length of the exposure of thelift-off resist layer to the developing solution to create a re-entrantstructure will vary based upon the baking time and temperature, and thisvariation is known in the art.

The textured pattern may be, for example, a re-entrant structure. Are-entrant structure refers, for example, to a structure that has atleast one internal angle that is greater than 180°. In addition, there-entrant structure may be an overhang re-entrant structure. There-entrant structure may be, for example, an individual re-entrantstructure or a continuous grooved structure.

Individual re-entrant structures are depicted in FIGS. 1 and 2. In anindividual re-entrant structure, the entirety of the developedphotoresist layer extends further in a direction parallel with thesubstrate than the textured lift-off resist layer, such that thephotoresist material overhangs the underlying lift-off resist layermaterial. The individual re-entrant structures may have any suitablespacing, density or solid area coverage on the substrate. For example,the individual re-entrant structures may have a solid area coverage offrom about 0.5% to about 80%, or from about 1% to about 50% of thesubstrate. The individual re-entrant structures may be spaced, forexample, 0.5 μm to about 10 μm, from about 1 μm to about 8 μm, or fromabout 2 μm to about 5 μm apart when measure from the centers of theindividual re-entrant structures.

A continuous re-entrant grooved structure is depicted in FIG. 4. Thegrooved structure may act as a channel for a drop, for example, an inkdrop, to flow through. A continuous re-entrant groove structure mayextend from one edge of the substrate to the opposite edge of thesubstrate. In a continuous re-entrant structure, at least a portion ofthe developed photoresist layer extends further in a direction parallelwith the substrate than the developed lift-off resist layer. Thecontinuous re-entrant structures may have any suitable spacing, densityor solid area coverage on the substrate. For example, the continuousre-entrant structures may have a solid area coverage of from about 1% toabout 80%, from about 1% to about 50%, or from about 2% to about 30% ofthe substrate. The continuous re-entrant structures may be spaced, forexample, from about 0.5 μm to about 10 μm, such as from about 1 μm toabout 8 μm, or from about 2 μm to about 6 μm, apart when measured fromthe centers of the re-entrant structures. The continuous groovestructure can have any suitable length. For example, the groovestructure may have a length of at least about 3 times of the width, suchas at least about 4 times of the width, or at least about 5 times of thewidth.

In addition, for either an individual re-entrant structure or acontinuous re-entrant structure, after development, the length of anundercut may be, for example, about 0.1 microns to about 5 microns, suchas from about 0.5 microns to about 4 microns, or from about 1 micron toabout 3 microns. The undercut results in at least a portion of thephotoresist layer extending beyond at least a portion of the lift-offresist layer.

The individual re-entrant structures or the continuous re-entrant groovestructure may have any suitable or desired height. Height, refers, forexample, to a direction that is perpendicular to the substrate, but doesnot pass through the substrate. For example, the re-entrant structuresmay have a height of from about 0.1 to about 10 microns, such as fromabout 0.2 to about 5 microns, or from about 0.5 to about 3 microns.

In addition, after development of the lift-off resist layer, thelift-off resist layer of the individual re-entrant structures or thecontinuous re-entrant groove structure may have any suitable thickness.Thickness refers, for example, to at least one direction that isparallel to the substrate. The thickness of the lift-off resist layer,after development, may be from about 0.1 microns to about 10 microns,such as from about 0.2 microns to about 5 microns, or from about 0.5microns to about 3 microns.

Etching may also be used to further refine the geometry of there-entrant structure. For example, the photoresist layer of the formedre-entrant structure may be etched to reduce the height of the overallstructure. Alternatively, the substrate or the silicon layer may beetched in order to increase the height of the overall structure.

Etching may occur by any known process. For example, etchants include ahydrofluoric acid etching solution or a plasma gas etch, such as anoxygen plasma etch. During the etching process, for example, for anoxygen plasma etchant, the oxygen plasma reacts with the polymericphotoresist and forms volatile compounds such as CO₂ or H₂O, thusreducing the photoresist height.

After the surface texture is created on the substrate or the siliconlayer, the textured pattern may be chemically modified. Chemicallymodifying the textured pattern refers, for example, to any suitablechemical treatment of the substrate that provides or enhances theoleophobic quality of the textured pattern. Chemically modifying thetextured pattern creates a superoleophobic surface on the texturedpattern. Chemically modifying the textured substrate may includechemical modification by a conformal self-assembling fluorosilanecoating onto the textured surface. The term “conformal” refers, forexample, to a coating designed to conform to the surface of an articleor structures being coated. For example, a conformal oleophobic coatingmay be formed conforming to the textured surface depicted in FIG. 1 or4, for example, by conforming to each exposed surface of the texturedsurface including all of the exposed surfaces of the patterned layersand all of exposed surfaces of the substrate. The conformal oleophobiccoating may have a thickness substantially uniform on these exposedsurfaces.

Any known method may be used to dispose the chemical modifier onto thesurface of the textured pattern. For example, the chemical modifier maybe disposed onto the surface of the textured pattern via a molecularvapor deposition technique, a chemical vapor deposition technique,E-beam, sputtering technique, for example, a vapor-phase silanizationtechnique, or a solution self-assembly technique.

For example, the chemically modifying may comprise disposing a chemicalmodifier, for example, a fluorosilane layer, onto the surface of thetextured pattern. The fluorosilane layer may be, for example synthesizedfrom, tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane,tridecafluoro-1,1,2,2-tetrahydrooctyltrimethoxysilane,tridecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilane,heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane,heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane,heptadecafluoro-1,1,2,2-tetrahydrodecyltriethoxysilane,fluorodecyltrichlorosilane (FDTS), and the like, or combinationsthereof.

Chemically modifying the textured substrate may also include solutioncoating a conformal amorphous fluoropolymer onto the textured surface.For example, the amorphous fluoropolymer may be a copolymer that iscopolymerized from tetrafluoroethylene (TFE) and2,2-bis-trifluoromethyl-4,5-difluoro-1,3-dioxole (BDD) monomers. Themolar ratio of TFE:BDD in the amorphous fluoropolymer coating can bebetween 5:95 and 50:50, or between 10:90 and 45:55, or between 15:85 and36:64. Examples of the conformal amorphous fluoropolymer coating includeDuPont Teflon AF1600 and AF2400 or a perfluoropolyether polymer suchFluorolink-D, Fluorolink-E10H or the like from Solvay Solexis.

Two states are commonly used to describe the composite liquid-solidinterface between liquid droplets on chemically modified texturedpattern, the Cassie-Baxter state and the Wenzel state. Static contactangles for a droplet at the Cassie-Baxter state (θ_(CB)) and the Wenzelstate (θ_(W)) are given by equations (1) and (2), respectively.

cos θ_(CB) =R _(f) f cos θ_(γ) +f−1  (1)

cos θ_(W) =r cos θ_(γ)  (2)

where f is the area fraction of projected wet area, R_(f) is theroughness ratio on the wet area and R_(f)f is solid area fraction, r isthe roughness ratio, and θ_(γ) is the contact angle of the liquiddroplet with a flat surface.

In the Cassie-Baxter state, the liquid droplet “sits” primarily on airand partially on solid asperities with a very large contact angle(θ_(CB)). According to the equation, liquid droplets will be in theCassie-Baxter state if the liquid and the surface have a high degree ofliquid repellency, for example, when θ_(γ)≧90°.

With respect to hydrocarbon-based liquid, for example, an ink, forexample, hexadecane, the textured pattern comprising overhang re-entrantstructures formed on the top surface of the structure renders thesurface “liquid repellent” enough (that is, θ_(γ)=73°) to result in thehexadecane droplet forming the Cassie-Baxter state at the liquid-solidinterface of the textured, oleophobic surface. However, as theoleophobicity of the surface coating decreases, the textured surfaceactually transitions from the Cassie-Baxter state to the Wenzel sate.The combination of surface texture and chemical modification, forexample, FDTS coating on the surface of the textured pattern, results inthe textured surface becoming superoleophobic.

FIG. 9 depicts a static contact angle for hexadecane on afluorosilane-coated textured surface comprising overhang re-entrantstructures. The contact angle for the hexadecane is 151°. Thisillustrates the liquid is in the Cassie-Baxter non-wetting state on thetextured surface. While not wishing to be bound by theory, it isbelieved that the re-entrant structure in combination with thefluorosilane coating imparts the superoleophobicity property.

The device having superoleophobic surfaces herein may be prepared, forexample, using roll-to-roll web fabrication technology. This processgenerally comprises creating a flexible device having a superoleophobicsurface on a roll comprising a flexible substrate, for example,polyimide. Roll-to-roll processing has the advantage of being acontinuous process as the substrate advances from the first station tosubsequent, downstream stations. For example, a roll comprising aflexible substrate passes through a first station wherein a layer ofamorphous silicon may be deposited on the flexible substrate, such as bychemical vapor deposition or sputtering. As described above, depositionof a silicon layer is not a necessary step of the process, and thisstation may be omitted. At a second station downstream from the optionalfirst station, a lift-off resist layer is coated on the substrate or, ifpresent, on the silicon layer. For example, the lift-off resist layermay be slot die coated, after which, at a third station, a photoresistlayer is coated onto the lift-off resist layer, followed by a fourthstation comprising a masking and exposing/developing station to create atextured pattern. The textured, flexible substrate may then pass througha coating station wherein the textured, flexible substrate can bemodified with an oleophobic coating.

The superoleophobic surfaces described herein may be particularlysuitable for use as front face materials for ink jet printheads.

As described above, fluid ink jet systems typically include one or moreprintheads having a plurality of ink jets from which drops of fluid areejected towards a recording medium. By selectively activating theactuators of the ink jets to eject drops as the recording medium and/orprinthead assembly are moved relative to one another, the depositeddrops can be precisely patterned to form particular text and graphicimages on the recording medium. MEMSJet drop ejectors consist of an airchamber under an ink chamber, with a flexible membrane in-between.Voltage is applied to an electrode inside the air chamber, attractingthe grounded flexible membrane downward, increasing the volume of theink chamber and thus lowering its pressure. This causes ink to flow intothe ink chamber from the ink reservoir. The electrode is then groundedand the membrane's restoring force propels it upward, creating apressure spike in the ink cavity that ejects a drop from the nozzle. Anexample of a full width array printhead is described in U.S. Pat. No.8,132,892, which is hereby incorporated by reference herein in itsentirety. An example of an ultra-violet curable gel ink which can bejetted in such a printhead is described in U.S. Pat. No. 7,714,040,which is hereby incorporated by reference herein in its entirety. Anexample of a solid ink which can be jetted in such a printhead is theXerox Color Qube™ cyan solid ink available from Xerox Corporation. U.S.Pat. No. 5,867,189, which is hereby incorporated by reference herein inits entirety, describes an ink jet print head including an ink ejectingcomponent which incorporates an electropolished ink-contacting ororifice surface on the outlet side of the printhead.

EXAMPLES

The purpose of the following examples is to illustrate re-entrantstructures made from a lift-off resist layer and a photoresist layer.

Example 1

The process disclosed herein was used to make the overhang re-entrantstructures depicted in FIG. 1. A lift-off resist layer of PMGIspin-coated on to a silicon wafer. The lift-off resist layer was bakedon a hotplate for five minutes at 180° C. A photoresist layer 102(Shipley 1805) was spin-coated over the baked lift-off resist layer. Thelayered structure was baked for 45 seconds at 115° C. After baking, aportion of the layered structure was then exposed to UV radiation at 436nm wavelength using a 5× stepper, for example, a GCA 6300 DSW ProjectionMask Aligner, and then developed for 45 seconds in a tetra-methylammonium hydroxide based developer, for example, AZ 300 MIF PhotoresistDeveloper from AZ Electronic Materials. A rinse in deionized waterimmediately after development was performed. In the above-describedprocess, the lift-off resist layer was not influenced by the UVradiation exposure and the development of the photoresist layer. Thedevelopment of the lift-off layer creates an undercut structure, thuscreating an overhang re-entrant structure. The photoresist layer extendsbeyond the lift-off resist layer in a direction parallel to thesubstrate.

After creation of the overhang re-entrant structure, the surface of theoverhang structure was chemically modified withfluorodecyltrichlorosilane (FDTS). FDTS was disposed on the surface ofthe textured pattern by vapor-phase salinization, although preferablythe fluoropolymer is disposed on the surface of the textured pattern bydip coating. The dip coating can be carried out in a fluoropolymersolution, which can be a mixture of DuPont TEFLON AF1600 and FC-75fluorinated solvent from 3M, at a volume ratio of about 1:5. Followingthe dipping, the film can be air-dried for several minutes and thendried in oven at about 112° C.

Example 2

FIG. 5 graphically depicts a lift-off resist layer 100 of PMGI (LOR 7Bby MicroChem) spin-coated onto a silicon wafer 101. The lift-off resistlayer 100 was baked on a hotplate for five minutes at 180° C. FIG. 6shows a photoresist layer 102 (SU-8 2000.5) was spin-coated over thebaked lift-off resist layer. In FIG. 7, the layered structure was bakedfor 60 seconds at 95° C. After baking, a portion 103 of the layeredstructure was then exposed to UV radiation at 436 nm wavelength using a5× stepper, for example, a GCA 6300 DSW Projection Mask Aligner, andbaked again for 60 seconds at 95° C.

FIG. 8 depicts the result of a two-step development. The exposedphotoresist layer was first developed for 60 seconds in solvent-baseddeveloper such as ethyl lactate or diacetone alcohol, for example, SU-8developer from MicroChem. A rinse in isopropanol after development ispreferred. In the above-described process, the lift-off resist layer wasnot influenced by the UV radiation exposure and the development of thephotoresist layer. The lift-off resist layer was subsequently developedfor 10 seconds in a tetra-methyl ammonium hydroxide based developer, forexample, AZ 300 MIF Photoresist Developer from AZ Electronic Materials,to create an undercut. The creation of the undercut results in anoverhang re-entrant structure. A rinse in deionized water afterdevelopment is preferred. As illustrated in FIG. 8, the photoresistlayer extended about 5 μm in a direction parallel to the substrate andthe lift-off resist layer extended approximately 4 μm in a directionparallel to the substrate.

The chemical modification was performed of the surface of the overhangstructure was performed as described in Example 1.

The textured patterned structures herein, for example, individualre-entrant structures, can have any suitable shapes and patterns. Theoverall textured structure can have or form a configuration designed toform a specific pattern. For example, in embodiments, the individualre-entrant structure or continuous groove structure can be formed tohave a configuration selected to direct a flow of liquid in a selectedflow pattern.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also,various presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art, and are also intended to beencompassed by the following claims.

What is claimed is:
 1. A front face for an ink jet printhead, the frontface comprising: a flexible substrate, wherein the flexible substratecomprises a plastic film; a lift-off resist layer; a photoresist layer,wherein the lift-off resist layer and the photoresist layer form atextured pattern, wherein the textured pattern comprises at least oneoverhang re-entrant structure; and a conformal fluoropolymer orfluorosilane coating disposed on a surface of the textured pattern. 2.The front face according to claim 1, wherein the conformal coating isselected from the group consisting of fluorosilane layers synthesizedfrom tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane,tridecafluoro-1,1,2,2-tetrahydrooctyltrimethoxysilane,tridecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilane,heptadecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane,heptadecafluoro-1,1,2,2-tetrahydrooctyltrimethoxysilane, andheptadecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilane, aperfluoropolyether polymer and an amorphous fluoropolymer copolymerizedfrom tetrafluoroethylene and2,2-bis-trifluoromethyl-4,5-difluoro-1,3-dioxole, or combinationsthereof.
 3. The front face according to claim 1, wherein the lift-offresist layer comprises poly(methyl methacrylate).
 4. The front faceaccording to claim 1, wherein the lift-off resist layer comprisespolymethylglutarimide.
 5. The front face according to claim 1, whereinthe textured pattern has a solid area coverage of about 0.5% to about80% of the substrate.
 6. The front face according to claim 1, whereinthe texture pattern comprises overhang re-entrant structures, whereinthe overhang re-entrant structures have height of about 0.1 microns toabout 10 microns.
 7. The front face according to claim 1, wherein thetexture pattern comprises overhang re-entrant structures, wherein theoverhang re-entrant structures have a thickness of about 0.1 microns toabout 10 microns.
 8. The front face according to claim 1, wherein thetextured pattern is an overhang re-entrant structure with an undercut ofabout 0.1 microns to about 5 microns.
 9. The front face according toclaim 1, wherein the overhang re-entrant structure is an individualre-entrant structure or a continuous grooved structure.
 10. The frontface according to claim 9, wherein the individual re-entrant structuresare spaced from about 0.5 μm to about 10 μm apart when measured from thecenters of the individual re-entrant structures.
 11. The front faceaccording to claim 9, wherein the continuous groove structures have alength of at least about 3 times of the width.
 12. The front faceaccording to claim 1, wherein the lift-off resist layer has a thicknessof from about 0.1 microns to about 10 microns.
 13. The front faceaccording to claim 1, wherein a static contact angle for hexadecane onthe conformal coating is
 151. 14. A front face for an ink jet printhead,the front face comprising: a flexible substrate, wherein the flexiblesubstrate comprises a plastic film; a lift-off resist layer; aphotoresist layer, wherein the lift-off resist layer and the photoresistlayer form a textured pattern, wherein the textured pattern comprises atleast one overhang re-entrant structure; and a conformal fluoropolymeror fluorosilane coating disposed on a surface of the textured pattern,wherein a hydrocarbon-based ink forms a contact-angle with a surface ofthe conformal coating disposed on the surface of the textured patternthat is greater than about 150°.
 15. A flexible device comprising aflexible substrate having a superoleophobic surface, wherein theflexible substrate comprises a plastic film; a lift-off resist layer; aphotoresist layer, wherein the lift-off resist layer and the photoresistlayer form a textured pattern, wherein the textured pattern comprises atleast one overhang re-entrant structure; and a conformal fluoropolymeror fluorosilane coating disposed on a surface of the textured pattern,wherein the conformal coating disposed on the surface of the texturedpattern comprises a superoleophobic surface.
 16. The flexible deviceaccording to claim 15, wherein the conformal coating is selected fromthe group consisting of fluorosilane layers synthesized fromtridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane,tridecafluoro-1,1,2,2-tetrahydrooctyltrimethoxysilane,tridecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilane,heptadecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane,heptadecafluoro-1,1,2,2-tetrahydrooctyltrimethoxysilane, andheptadecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilane, aperfluoropolyether polymer and an amorphous fluoropolymer copolymerizedfrom tetrafluoroethylene and2,2-bis-trifluoromethyl-4,5-difluoro-1,3-dioxole, or combinationsthereof.
 17. The flexible device according to claim 15, wherein thelift-off resist layer is a poly(methyl methacrylate) or apolymethylglutarimide layer.
 18. The front face according to claim 15,wherein the textured pattern has a solid area coverage of about 0.5% toabout 80% of the substrate.
 19. The front face according to claim 15,wherein the conformal coating comprises a copolymer that iscopolymerized from tetrafluoroethylene (TFE) and2,2-bis-trifluoromethyl-4,5-difluoro-1,3-dioxole (BDD) monomers.
 20. Thefront face according to claim 15, wherein the overhang re-entrantstructure is an individual re-entrant structure or a continuous groovedstructure.